When vertically oriented processing columns or vessels are provided with internal valve control, the valves are quite large and cumbersome to handle. Under circumstances where valve repair is required, the processing vessel must be taken out of service for an extended period and at least partially disassembled so that the valve can be removed and repaired or replaced. As a further disadvantage, the valve or valves may be positioned in the upper portion of an upstanding processing vessel and therefore may be located at a substantially elevated position above the support base of the vessel. It is generally necessary to employ a special portable crane mechanism to assist in removing and replacing the valve and for removing and replacing any other structure that must be removed to facilitate removal of the valve. Obviously, any requirement for special equipment such as cranes and any procedure that requires partial disassembly of a processing vessel and renders the processing vessel unserviceable for an extended period is of extremely expensive nature and is detrimental to commercial production of the vessel. It is desirable, therefore, to provide a valve mechanism that may be simply and efficiently repaired without any requirement for disassembling the process vessel or effecting complete removal of the valve to facilitate the repair procedure.
Where butterfly valves and other valves having annular seats are provided for service conditions involving a wide variation of heat and especially where very large valves are subjected to high temperature service, such as when used in processing vessels, fixed valve seat structures of such valves can become damaged any fractured by differential stresses that occur as the valve bodies expand and contract responsive to thermal variations. Under condtions where large valve bodies are composed of relatively thin material and have internal structural means defining an annular seat, it is quite possible that the internal stresses that are induced into the valve body by heat induced expansion or contraction of the differing masses that comprise the valve body may cause the valve body to fail. Large internal masses defined by typical annular valve seats become heated much more slowly as compared to relatively thin valve bodies and tend to expand and contract at different rates as compared to the valve body walls. When this occurs, the material at the juncture between the valve body walls and seat mass portion of the valve body structure can become excessively stressed, resulting in failure of the valve body. It is desirable, therefore, to provide means for ensuring against the development of internal stresses in the vicinity of the valve seat responsive to the temperature variations to which the valve might be subjected.
In most cases where butterfly valves are concerned, the valve closure element is a single integral disc element that is positioned in transverse relation to the flow path of the valve in a closed position thereof and is positioned in substantially parallel relation to the flow path in its open position. Peripheral sealing is typically accomplished by engagement at the external periphery of the disc element with resilient sealing members. Where high temperature valve service is expected, typical elastomeric valve seat members are not capable of functioning for extended periods of time if at all due to the adverse effects of the high temperature involved.
Butterfly valves are not widely accepted in high temperature service because of the difficulty in obtaining proper sealing while at the same time providing a valve mechanism that is effectively responsive under the adverse conditions of high temperature service. In most cases it is necessary to choose valves other than butterfly valves for high temperature service and thereby lose the efficiency that is typically a primary purpose in choosing butterfly valves for controlling the flow of fluids. The typical metal-to-metal sealing that is frequently desirable in high temperature service conditions is not ordinarily attainable in conventional butterfly valve mechanisms and, therefore, users are typically restricted to other kinds of valves when high temperature service is expected. Examples of a dual closure type butterfly valve that is capable of high temperature service are evidenced by U.S. Pat. Nos. 3,533,438 and 3,384,112 of Smith. Other similar valves are shown in U.S. Pat. Nos. 3,241,568 of Mayo, Jr., 3,179,164 of Heller et al and 4,038,734 of Goldman.
Especially under conditions where valves are to be utilized in high temperature service, it is necessary to repair the valves on more frequent occasions as compared to service conditions where normal operating temperatures are encountered. It is also desirable under such conditions to provide valves that are capable of being repaired while in place in the processing vessel in order that it is not necessary to disassemble the vessel in order to service the valve. It is desirable to repair the valves without unnecessary delay in order that the processing vessel can be placed back in service with minimal down time. In view of the fact that most butterfly valves must be completely removed from the processing vessel for repair or replacement, butterfly valves typically present obstacles to accomplishing repair with minimum down time. It is desirable, therefore, to provide a valve mechanism having the operational capability of a butterfly valve and yet being capable of repair without necessitating removal of the valve body from the processing vessel. Accordingly, it is a primary feature of the present invention to provide a novel butterfly valve mechanism having dual closure elements which is capable of being repaired without removal of the valve body from the line.
It is also a feature of the present invention to provide a dual closure type butterfly valve that is readily adapted to service conditions where wide variations in temperature are to be expected.
It is another feature of this invention to provide a novel dual closure type butterfly valve mechanism incorporating a seat assembly that is not subjected to circumferential stressing as the valve body is subjected to considerable expansion and contraction due to heat fluctuation during service conditions.
It is another important feature of this invention to provide a novel dual closure type butterfly valve mechanism for process vessels and the like wherein an offset access opening is defined by the valve body and the closure and closure support structures of the valve are capable of being positioned for effective removal through the access opening, thereby enabling a valve mechanism to be effectively serviced without removal of the valve body from the process vessel and thereby promoting minimal down time for valve repair.
It is an even further feature of this invention to provide a novel dual closure type butterfly valve mechanism wherein minimal turbulence is created in the fluid flowing through the full valve while the valve mechanism is being maintained in the open position thereof and wherein minimum hydraulic losses occur in the flowing fluid responsive to differential pressure across the open valve mechanism.
Other and further objects, advantages and features of this invention will become obvious to one skilled in the art upon an understanding of the illustrative embodiment about to be described and various advantages, not referred to herein, will occur to one skilled in the art upon employment of the invention in practice.